Field of the Invention
The present invention relates to a membrane electrode assembly containing a solid polymer electrolyte membrane and electrodes disposed on either side thereof, wherein each of the electrodes contains an electrode catalyst layer and a gas diffusion layer, and at least one of the electrodes further contains a porous layer between the electrode catalyst layer and the gas diffusion layer.
Description of the Related Art
In a solid polymer fuel cell, a membrane electrode assembly is interposed between a pair of separators to form a unit cell. The membrane electrode assembly contains an ion-exchange polymer electrolyte membrane, an anode facing one surface of the membrane, and a cathode facing the other surface of the membrane.
Each of the anode and the cathode has an electrode catalyst layer and a gas diffusion layer. The electrode catalyst layer is disposed facing the electrolyte membrane, and acts as a reaction field of an electrode reaction. The gas diffusion layer acts to diffuse and supply a reactant gas to the electrode catalyst layer. In general, the gas diffusion layer is composed of a carbon paper or the like. Therefore, for example, a fiber in the gas diffusion layer may be stuck into the electrolyte membrane to physically deform the membrane. In this case, the electrolyte membrane may be deteriorated, and the gas barrier property against the reactant gas may be lowered. Thus, it is necessary to prevent the physical deformation of the electrolyte membrane.
In view of preventing the sticking of the fiber in the gas diffusion layer into the electrolyte membrane through the electrode catalyst layer, for example, in Japanese Laid-Open Patent Publication No. 2010-040377, electrolyte-rich portions are discontinuously arranged in the stacking direction of the electrode catalyst layer, whereby the electrode catalyst layer exhibits a strong binding property in the plane direction.
In general, in the membrane electrode assembly, the overall size (surface area) of the electrode catalyst layer is smaller than that of the electrolyte membrane. Thus, the outer peripheral edge of the electrolyte membrane is exposed on the outside of the electrode catalyst layer. Consequently, for example, in production of the membrane electrode assembly, when the gas diffusion layer is thermally compression-bonded to the electrolyte membrane, the fiber in the gas diffusion layer may be disadvantageously stuck into the outer peripheral edge of the electrolyte membrane.
In view of solving the problem, for example, in Japanese Laid-Open Patent Publication No. 2010-146769, a reinforcement member is used for preventing the periphery of the gas diffusion layer from being brought into direct contact with the electrolyte membrane. Specifically, only two opposite sides of the electrolyte membrane are exposed on the outside of the electrode catalyst layer, and the reinforcement member is disposed on each of the two sides to prevent the sticking of the fiber in the diffusion layer.
However, in the technologies of Japanese Laid-Open Patent Publication Nos. 2010-040377 and 2010-146769, as described above, the membrane electrode assembly has a complicated structure containing the specially-configured electrode catalyst layer or electrolyte membrane. Thus, the technologies are disadvantageous in low membrane electrode assembly productivity and increased production cost. In view of avoiding the problem, for example, as described in Japanese Laid-Open Patent Publication No. 2005-332672, a reinforcement layer may be interposed between the electrolyte membrane and the electrode catalyst layer to prevent the sticking of the fiber in the diffusion layer into the electrolyte membrane.